1. Field of the Invention
The present invention relates to a starter loaded on an automobile, for example.
This application claims priority to and the benefit of Japanese Patent Application No. 2011-260627 filed on Nov. 29, 2011, and Japanese Patent Application No. 2012-214804 filed on Sep. 27, 2012, the disclosures of which are incorporated herein by reference.
2. Background Art
In the related art, as a starter used for starting the engine of an automobile, when start the engine, a jump-in type starter which starts the engine by jumping in the pinion gear toward the ring gear to mesh with the ring gear and driving the ring gear by the pinion gear, is known (for example, see Japanese Unexamined Patent Application, First Publication No. 2002-130097).
Recently, in order to improve the quietness or fuel efficiency of a vehicle, the number of vehicles is increasing which are provided with a so-called idle stop function for turning off the engine momentarily when the vehicle is stopping temporarily.
The starter described in Japanese Unexamined Patent Application, First Publication No. 2002-130097 can be applied even to vehicles provided with the above-mentioned idle stop function. In the starter described in Japanese Unexamined Patent Application, First Publication No. 2002-130097, a driving shaft (an output shaft) is connected to a rotor shaft of a starting motor through a planetary gear type reducer. Both ends of the driving shaft in the axial direction are rotatably supported in a housing of the starter. A mover which moves forward and backward in the axial direction through a lever by a magnet switch (an electromagnetic device) is spline-engaged to the driving shaft. Further, a pinion gear is installed in the driving shaft movably forward and backward in the axial direction toward the ring gear.
The ring gear and pinion gear are formed of helical gears. The twisting direction of the teeth of the ring gear and pinion gear is set in such a way that the thrust load of the jumping-in direction acts on the pinion gear while the pinion gear is driving the ring gear.
According to Japanese Unexamined Patent Application, First Publication No. 2002-130097, once the pinion gear is meshed with the ring gear, the pinion gear receives the thrust load generated due to the twisting angle of the teeth of both gears and moves on by itself in the jumping-in direction, thereby the meshing performance of the pinion gear with respect to the ring gear is improved.
Meanwhile, in the starter described in Japanese Unexamined Patent Application, First Publication No. 2007-71043, a second plunger unit is arranged movably forward and backward in the axial direction by a magnet switch (an electromagnetic device) installed coaxially with a driving shaft (an output shaft). A pinion gear is installed on the driving shaft movably forward and backward in the axial direction toward the ring gear.
In general, the housing of starter is made by die-cast molding of aluminum material. But in the above-described related art, when the mover is sliding toward the ring gear by receiving the thrust load generated from the helical gear, thrust load is generated even on the output shaft connected to the mover. Thus, because the output shaft is sliding toward the ring gear, there is a possibility of sliding contact between one side end face of the output shaft and the housing. Accordingly, because an abutting impact when the output shaft slides to abut the housing or a rotary force (a frictional force) of the output shaft after abutting is applied to the housing, it is necessary to improve the durability of housing. So it is also considered that the material of housing is changed to a high-grade member, or the thickness of housing is made thick. But it entails an increase of starter cost or the starter becoming bigger.
Especially in vehicles provided with an idle stop function, engine stop/start is made frequently, and the frequency of use becomes higher than that of an ordinary starter. Therefore, the best scheme of improvement is in demand for the above-mentioned task.